Aging or acute loss of estrogens or androgens increases the levels of reactive oxygen species, activates nuclear factor-κB (NF-κB), and promotes the phosphorylation of p66^shc, a redox enzyme that amplifies mitochondrial reactive oxygen species generation and stimulates apoptosis. We report that in mesenchymal progenitor and osteoblastic cell models, H₂O₂ activated a protein kinase C (PKC)β/p66^shc/NF-κB signaling cascade and that p66^shc was an essential mediator of the stimulating effects of H₂O₂ on the apoptosis of osteoblastic cells as well as their ability to activate NF-κB. 17β-Estradiol (E₂) or the nonaromatizable androgen dihydrotestosterone abrogated the effects of H₂O₂ on p66^shc and NF-κB activation by attenuating the phosphorylation of the redox-sensitive cytoplasmic kinase PKCβ. Additionally, both E₂ and dihydrotestosterone prevented H₂O₂-induced apoptosis by a mechanism that involved attenuation of p66^shc resulting from decreased phosphorylation of PKCβ. Consistent with a kinase-mediated mechanism of sex steroid action, the effects of E₂ were reproduced by a polymeric form of estradiol that is not capable of stimulating the nuclear-initiated actions of ERα. These results demonstrate that p66^shc is an essential mediator of the effects of oxidative stress on osteoblastic cell apoptosis, NF-κB activation, and cytokine production. The ability of either estrogen or androgen to attenuate the effects of oxidative stress on osteoblastic cell apoptosis, NF-κB activation, and cytokine production results from their common property to suppress PKCβ-induced p66^shc phosphorylation via a mechanism that does not require stimulation of the nuclear-initiated actions of sex steroids.